“I must be descending,” Bob Mould shouts on “The Descent,” but if so he isn’t going gently. The former Hüsker Dü and Sugar frontman’s new solo album Silver Age came out yesterday on Merge, and he stopped by Late Show With David Letterman last night for a blazing performance of the record’s scorching, power-pop advance track). Backed by Superchunk/Mountain Goats drummer Jon Wurster along with bassist Jason Narducy of Verbow and Spl:t S:ngle, Mould’s poignant tribute to the music “that gave people so much hope” even overcame their host’s initial delight in repeating Hüsker Dü’s name. “That is all you want right there,” Letterman ultimately enthused. Imagine how much fun he’d have saying Les Savy Fav’s name, but those indie rockers’ 2004 single “The Sweat Descends” seems relevant, too — it’s not all downhill, as long as you stay alive.